A clathrate hydrate means a crystalline compound in which guest molecules are not chemically bonded with each other but are physically captured and trapped in a three-dimensional lattice structure which is formed by a hydrogen bond between host molecules. A gas hydrate has a structure in which the host molecule is a water molecule and the guest molecule is a gas molecule having a low molecular weight such as methane, ethane, propane, and carbon dioxide.
The gas hydrate was first found by Sir Humphry Davy of England in 1810. He announced in the Bakerian Lecture of the Royal Society that when chlorine reacts with water, a compound having a similar form to ice is generated, but the temperature thereof is higher than 0° C. Michael Faraday first found in 1823 that a gas hydrate is generated by a reaction of 10 water molecules with one chlorine molecule.
Up to the present since then, academic study on the gas hydrate, which is one of the phase change materials (PCMs), has continued and the main content of the study has included phase balance and generation/dissociation condition, crystal structure, polycrystalline coexisting phenomenon, competitive composition change within a cavity, and the like and a minute study has been conducted in various microscopic and macroscopic aspects.
It has been known up to now that there are about 130 kinds of guest molecules which may be trapped in the gas hydrate and an example of the guest molecules may include CH4, C2H6, C3H8, CO2, H2, SF6, and the like. Further, gas hydrate crystal structures are configured to have a polyhedral cavity which is formed by hydrogen-bonded water molecules and the gas hydrate has a crystal structure of a body-centered cubic structure I (sI), a diamond cubic structure II (sII), and a hexagonal structure H (sH) depending on a kind and a generation condition of gas molecule. The sI and the sII are determined by the size of the guest molecule and in the sH, a size and form of the guest molecule is an important factor.
The guest molecule of the gas hydrate which naturally exists in the deep sea and permafrost areas is mainly methane, and methane has received attention as an environmentally-friendly clean energy source since emission of carbon dioxide (CO2) is small at the time of combustion. In detail, the gas hydrate may be used as an energy source which may replace traditional fossil fuel, as solid storage and transportation of natural gas using the hydrate structure, as isolation/storage of CO2 to prevent global warming, and in, in particular, a seawater desalination apparatus using a gas or aqueous solution separation technology, and therefore the utilizations thereof are very high.
The gas hydrate is frequently found in an area adjacent to a petroleum or natural gas reservoir and a coal seam or a low-temperature and high-pressure deep sea sediment, in particular, a continental slope area. Further, the gas hydrate may also be artificially manufactured and the existing apparatus for manufacturing a gas hydrate known up to now generally has a structure as illustrated in FIG. 1.
The most important process in the commercialization technology using the apparatus for manufacturing a gas hydrate may be considered to be the formation of hydrate and basically, in order to increase formation speed of the gas hydrate, there is a need to maximize the formation speed of the hydrate by increasing the contact area of gas, in a gaseous state, and water. Further, the process of primarily separating the water that did not react, from the formed gas hydrate slurry is very important.
FIG. 1a illustrates a typical apparatus 10 for manufacturing a gas hydrate according to the related art.
The apparatus 10 for manufacturing a gas hydrate according to the related art is configured to include a water feeder 1, a gas supplier 2, a reactor 3 in which water supplied from the water feeder 1 reacts with gas supplied from the gas supplier 2, a dehydrator 4 which discharges the gas hydrate generated in the reactor 3 to the outside, and an agitator 5 which increases a reaction speed of water and gas. To make the environment within the reactor 3 have temperature conditions appropriate for the manufacturing of gas hydrate, a separate cooling jacket 6 to enclose an outer side of the reactor 3 may be provided. The cooling jacket 6 is connected to a refrigerant supplier 7 and thus may be continuously supplied with a refrigerant.
In the aspect of the above-mentioned manufacturing apparatus 10 of the related art, the water and the gas supplied to the reactor 3 are mixed by the agitator 5 and thus the reactivity is increased, but in this case, a problem exists where the apparatus 10 may perform only simple mixing activities but does not have the mechanism to rapidly propagate a water molecule into a gas molecule.
In addition, the dehydrator 4 is generally disposed at a lower portion or a side of the reactor 3, but a problem exists where it is difficult to directly obtain a high-purity gas hydrate from the reactor 3 by separating water from the gas hydrate slurry, which is generated in such a state.